Certain 9-(.beta.-D-Ribofuranosyl) 6-substituted purines including the carboxamide, the thiocarboxamide and the carbonitrile are prepared and certain of these have been tested and found to have biological activity as an antiviral agent while others are useful as precursors in forming the biologically active compounds.
Over the last three decades medical science has discovered and learned to use chemotherapeutic agents having activity against microorganisms including bacterium and certain fungi. Excluded from this group have been agents which are active against viruses.
Viral infections are known to be one of the most frequent causes of human illness. Upwards of 300 different immunologic types of virus have been associated with humans; however, not all of these are identified with clinical recognizable diseases.
Many of these diseases, having once been acquired, render their host free from further infections by the same agent by stimulating a life-long immunologic response by the host to the viral agent. It is by this very same mechanism that conquest of certain virus-caused disease states has been achieved. By using prophylaxis induced by either killed or attenuated viruses or infection with an immunologically related virus which causes a very mild disease state, vaccines have been developed, for smallpox, yellow fever, polio, and some of the common childhood diseases, e.g. mumps, rubella, and measles.
While prophylaxis from some viral diseases can be obtained by immunity, immunologic protection from other virual diseases is not possible because either prolonged immunity is not developed against the virus, or the same clinically described disease is caused by a large group of related viruses which are antigenically dissimilar and do not produce cross immunity, e.g. common cold viruses. Coupled with this lack of universal prophylaxis against all viral diseases is the necessity to effect a cure in an already established viral disease.
In the last few years research has been centered on finding effective chemotherapeutic antiviral agents. At present there are only a very few compounds known to be active against viruses. Included in this group are amantadine(1-adamantanamine), methisazone(1-methylisatin B-thiosemicarbazone), cytarabine (cytarabine (cytosine arabinoside), 6-IDU (5-iodo-2'-deoxyuridine); however, these agents are of either limited spectrum, e.g., amantadine is only active against Type A influenze virus, cytarabine and 5-IDU are not active against RNA viruses and they are quite toxic.